You are correct when you say that humans do not create most of the CO_2 in the atmosphere. In fact, we create roughly 4.5% of what is released into the atmosphere every year.  In numerical amounts, it's around 5.5 billion tons of carbon yearly due to fossil fuel burning, and 1.6 billion tons from deforestation.  The problem is that this 7.1 billion tons of carbon per year is more than the Earth's ecosystems, oceans, etc., can absorb back up - scientists believe these only account for some 2.0 billion tons. We directly measure that every year 3.2 billion tons of carbon (in the form of CO_2) stays in the atmosphere. There's another 1.9 billion tons of carbon unaccounted for, but we still have a the 3.2 billion we KNOW is going into the atmosphere.
Every year 3.2 billion tons of carbon is being added to the atmosphere. The carbon cycle was nicely balanced before humans came along burning fossil fuels.  Rather than reducing the amount of carbon that humans produce we could instead solve the problem by making all animals stop breathing, preventing any forest fires, stopping decomposition, and capturing all carbon released from the ocean. This is left as an exercise for the reader.
26 November 2005
Global Warming: the numbers
I was challenged in a locked post on the blog of foreverbeach to show some numerical proof that humans are making an impact on global warming. leenoox's argument was that cow farts contain more greenhouse gasses, and that humans contribute such a tiny amount it doesn't make a difference. I wrote an informative reply I wanted to post here.